Partial molar compressibilities of halogeno complexes of platinum and palladium in aqueous solutions at 25°C

Ultrasonic propagation velocities were measured at 25°C for dilute aqueous solutions of K2[PtX4], K2[PtX6], K2[PdX4], and K2[PdX6] (X = Cl, Br, or SCN). The data obtained were combined with our previous density data to calculate the adiabatic compressibilities of each solution. Then, the infinite dilution values of partial molar adiabatic compressibilitiesKos were evaluated. By subtraction of theKos (K+) from those of the complexes, the values ofKos for the halogeno complex ions [PtX4]2-, [PtX6]2-, [PdX4]2- and [PdX6]2- were determined. The values for the thiocyano complex ions [Pt(SCN)4]2- and [Pt(SCN)6]2- are positive, showing that the interaction of the ligand SCN- with the solvent water is very weak. Although the V2o behavior of the complex ions [PtCl6]2- and [PdCl6]2- differed only slightly, compressibility measurement has indicated that the ion [PdCl6]2- interacts more strongly than [PtCl6]2-.